The present invention relates to a device and to a method of applying a carrying handle to a pack.
Many consumer products come in the form of packs. A classic example is a multipack containing a number of bottles of water packed together under a plastic film. The term pack is therefore understood as referring to any product or set of products having a substantially parallelepipedal form.
For the purpose of transporting these packs, it is known practice to affix a handle thereto. This handle consists of a tape whose two ends are provided with an adhesive. The handle is therefore applied to the pack such that the two ends coated with adhesive stick onto the vertical walls of the pack, while the central part of the handle forms a grip by means of which the pack can be taken hold of and transported.
A very advantageous device for applying such a handle is known from document EP 560 699 or from document FR 2 787 416. This device uses a rotary arm which deposits and sections an adhesive tape supplied continuously to a pack. By virtue of its rotary arm, this device makes a very high application rate possible. At the moment when a handle is being applied, a label, that is to say a rectangular cardboard element (sometimes referred to as a strip), which may be used as an advertising medium, is generally attached to the tape.
However, this way of producing and applying a handle, that is to say using, on the one hand, an adhesive tape (transparent or translucent monochrome tape) and, on the other hand, a label attached at the moment of application, is now being increasingly replaced by a type of handle known as “prepared handle”.
The term prepared handle is intended to mean a handle which incorporates a label. In order to limit the number of feeders (tape feeders and label feeders), the labels are thus placed uniformly on the adhesive tape with a defined pitch, the tape being in the form of a reel.
With the use of a device such as that described in documents EP 560 699 or FR 2 787 416, the rotary arm determines the length of a handle, the length of the handle being dependent on the size of the pack.
Each pack therefore determines a handle length, which in turn determines a length of the rotary arm performing the ad hoc application and sectioning of the handle.
In the case of a so-called prepared handle, the reel of tape comprises a succession of handles arranged one behind the other.
Thus, it is imperative that the tape be sectioned to the exact nominal length of the handle, failing which the label is no longer centered with respect to the pack to which the handle is applied. Since the handles are arranged in series, an error in the positioning of a handle has repercussions on the application of the subsequent handles and may cumulate with other errors due to the elongation of subsequent handles.
It should be noted that this problem is specific to prepared handles; in the case of an attached label, the latter is supplied at the moment of application and cutting of the adhesive tape, that is to say independently of the application and cutting of the tape.
In the case of prepared handles, that is to say those incorporating labels distributed at predetermined fixed intervals and applied by a device with a rotary arm as shown in EP 560 699 or FR 2 787 416, it is found that a drift inevitably occurs in the application of the handles.
This drift is due particularly to the fact that, during the application, the rotary arm exerts a tension on the tape in order to apply it to the pack. To give a clearer idea, this tension can be set at around 7 daN. This tension varies as a function of each reel, particularly as a function of the degree of gluing or of the ambient temperature acting on the viscosity of the adhesive and as a function of the position at which the tape is drawn from the reel.
The tension exerted on the tape causes an elongation of the tape. The coefficient of elongation itself varies from one reel to another and, in practice, the elongation of the tape is between 0.5% and 1.5%.
One may take the example of an adhesive tape incorporating handles having a nominal length of 500 mm. The term nominal length is to be taken in its usual sense, that is to say the theoretical length announced by the tape manufacturer. As is customary, the manufacturer guarantees the nominal length with a tolerance range which is of the order of ±1 mm.
It will thus be understood that, with respect to the nominal length of 500 mm, the actual length of the applied handle may vary between two extreme values, namely 499×1.005=501.5 mm and 501×1.015=508.51 mm. The very significant consequence to be underlined is that the length of the tape varies in a non-reproducible manner, thereby making it impossible to determine, a priori, the elongation of the tape so that it can be incorporated into the length of the rotary arm.
These random variations in the length of the tape prevent, in practice, the application of prepared handles using a device with a rotary arm which, otherwise, would have a considerable benefit in terms of application rate.